In the prior art, these kinds of expansion valves were used in refrigeration cycles of air conditioners in automobiles and the like. FIG. 5 shows a prior art expansion valve in cross section together with an explanatory view of the refrigeration cycle. The expansion valve 10 includes a valve body 30 formed of prismatic-shaped aluminum comprising a refrigerant duct 11 of the refrigeration cycle having a first path 32 and a second path 34, the one path placed above the other with a distance in between. The 15 first path 32 is for a liquid-phase refrigerant passing through a refrigerant exit of a condenser 5 through a receiver 6 to a refrigerant entrance of an evaporator 8. The second path 34 is for a liquid-phase refrigerant passing through the refrigerant exit of the evaporator 8 toward a refrigerant entrance of a compressor 4.
An orifice 32a for the adiabatic expansion of the liquid refrigerant supplied from the refrigerant exit of the receiver 6 is formed on the first path 32. The orifice 32a is positioned on the vertical center line taken along the longitudinal axis of the valve body 30. A valve seat is formed on the entrance of the orifice 32a, and a valve means 32b supported by a valve member 32c. The valve means 32b and the valve member 32c are welded and fixed together. The valve member 32c is fixed onto the valve means 32b and is also forced by a spring means 32d, for example, a compression coil spring.
The first path 32 where the liquid refrigerant from receiver 6 is introduced is a path of the liquid refrigerant, and is equipped with an entrance port 321 and a valve room 35 connected thereto. The valve room 35 is a room with a floor portion formed on the same axis as the center line of the orifice 32a, and is sealed by a plug 39.
Further, in order to supply drive force to the valve body 32b according to an exit temperature of the evaporator 8, a small hole 37 and a large hole 38 having a greater diameter than the hole 37 is formed on said center line axis perforating through the second path 34. A screw hole 361 for fixing a power element member 36 working as a heat sensor is formed on the upper end of the valve body 30.
The power element member 36 is comprised of a stainless steel diaphragm 36a, an upper cover 36d and a lower cover 36h each defining an upper pressure activate chamber 36b and a lower pressure activate chamber 36c forming two scaled chambers above and under the diaphragm 36a, and a tube 36i for enclosing a predetermined refrigerant working as a diaphragm driver liquid into said upper pressure activate chamber, wherein said lower pressure activate chamber 36c is connected to said second path 34 via a pressure hole 36e formed to have the same center as the center line axis of the orifice 32a. A refrigerant vapor from the evaporator 8 is flown through the second path 34. The second path 34 is a path for gas phase refrigerant, and the pressure of said refrigerant vapor is added to said lower pressure activate chamber 36c via the pressure hole 36e.
Further, inside the lower pressure activate chamber 36c is a valve member driving shaft comprising a heat sensing shaft 36f and an activating shaft 37f The heat sensing shaft 36f made of aluminum is movably positioned through the second path 34 inside the large hole 38 and contacting the diaphragm 36a so as to transmit the refrigerant exit temperature of the evaporator 8 to the lower pressure activate chamber 36c, and to provide driving force in response to the displacement of the diaphragm 36a according to the pressure difference between the upper pressure activate chamber 36b and the lower pressure activate chamber 36c by moving inside the large hole 38. The activating shaft 37f made of stainless steel is movably positioned inside the small hole 37 and provides pressure to the valve means 32b against the spring force of the spring means 32d according to the displacement of the heat sensing shaft 36f The heat sensing shaft 36f is equipped with a sealing member, for example, an O ring 36g, so as to provide seal between the first path 32 and the second path 34. The heat sensing shaft 36f and the activating shaft 37f are contacting one another, and the activating shaft 37f is in contact with the valve member 32b. Therefore, in the pressure hole 36e, a valve member driving shaft extending from the lower surface of the diaphragm 36a to the orifice 32a of the first path 32 is positioned having the same center axis as the pressure hole.
A known diaphragm driving liquid is filled inside the upper pressure activating chamber 36b placed above a pressure activate housing 36d, and the heat of the refrigerant vapor from the refrigerant exit of the evaporator 8 flowing through the second path 34 via the diaphragm 36a is transmitted to the diaphragm driving liquid.
The diaphragm driving liquid inside the upper pressure activate chamber 36b adds pressure to the upper surface of the diaphragm 36a by turning into gas in correspondence to said heat transmitted thereto. The diaphragm 36a is displaced in the upper and lower direction according to the difference between the pressure of the diaphragm driving gas added to the upper surface thereto and the pressure added to the lower surface thereto.
The displacement of the center portion of the diaphragm 36a to the upper and lower direction is transmitted to the valve member 32b via the valve member driving shaft and moves the valve member 32b close to or away from the valve seat of the orifice 32a. As a result, the refrigerant flow rate is controlled.
That is, the gas phase refrigerant temperature of the exit side of the evaporator 8 is transmitted to the upper pressure activate chamber 36b, and according to said temperature, the pressure inside the upper pressure activate chamber 36b changes, and the exit temperature of the evaporator 8 rises. When the heat load of the evaporator rises, the pressure inside the upper pressure activate chamber 36b rises, and accordingly, the heat sensing shaft 36f or valve member driving shaft is moved in the downward direction and pushes down the valve means 32b via the activating shaft 37, resulting in a wider opening of the orifice 32a. This increases the supply rate of the refrigerant to the evaporator, and lowers the temperature of the evaporator 8. In reverse, when the exit temperature of the evaporator 8 decreases and the heat load of the evaporator decreases, the valve means 32b is driven in the opposite direction, resulting in a smaller opening of the orifice 32a. The supply rate of the refrigerant to the evaporator decreases, and the temperature of the evaporator 8 rises.
In a refrigeration system using such expansion valve, a so-called hunting phenomenon wherein over supply and under supply of the refrigerant to the evaporator repeats in a short term is known. This happens when the expansion valve is influenced by the environment temperature, and, for example, the non-evaporated liquid refrigerant is adhered to the heat sensing shaft of the expansion valve. This is sensed as a temperature change, and the change of heat load of the evaporator occurs, resulting in an oversensitive valve movement.
When such hunting phenomenon occurs, it not only decreases the ability of the refrigeration system as a whole, but also affects the compressor by the return of liquid to said compressor.
The present applicant suggested an expansion valve shown in FIG. 6 as Japanese Patent Application No. H7-325357. This expansion valve 10 includes a resin 101 having low heat transfer rate being inserted to and contacting the heat sensing shaft 100 forming an aluminum valve member driving shaft. A PPS resin which will not be affected by the refrigerant and the like is used as the low heat transfer rate resin 101.
Said resin 101 is not only mounted on the portion of the heat sensing shaft 100 being exposed to the second path 34 where the gas phase refrigerant passes, but also on the heat sensing portion existing inside the lower pressure activate chamber 36c. The thickness of the resin 101 can be about 1 mm.
Further, it should be understood that the resin 101 could only be mounted on the exposed portion of the heat sensing shaft 100 to the second path 34.
By mounting such resin 101, when the non-evaporated refrigerant fiom the evaporator flows through the second path 34, and adheres to the heat sensing shaft of the expansion valve, the heat transfer rate of the resin 101 is low, so the change in heat load of the evaporator or increase of the heat load of the evaporator occurs, the response ability of the expansion valve 10 is low, and the hunting phenomenon of the refrigeration system is avoided.
The problem of the above-explained expansion valve is that it is expensive to produce such valve because there is a need to attach the resin 101 to the aluminum heat sensing shaft 100 in the manufacturing, process.
The object of the present invention is to provide a cost effective expansion valve which avoids the occurrence of hunting phenomenon in the refrigeration system with a simple change in structure.